Like protozoans, extremely unusual in college wine vault (11)

I believe the answer is:

unicellular

I'm a little stuck... Click here to teach me more about this clue!

'like protozoans extremely' is the definition.
I can't tell whether this defines the answer.

'unusual in college wine vault' is the wordplay.
'unusual' becomes 'lu' (I can't justify this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'college' becomes 'uni' (short for university).
'wine vault' becomes 'cellar' (I've seen this before).
'uni'+'cellar'='unicellar'
'lu' put inside 'unicellar' is 'UNICELLULAR'.

Can you help me to learn more?

(Another definition for unicellular that I've seen is " Simple".)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app